Arrhythmias refer to the disruption of the natural heart rhythm. This irregular heart rhythm causes the heart to suddenly stop pumping blood. Atrial pathologies are the most common arrhythmias with atrial fibrillation and atrial flutter being the most prevalent. The number of individuals with atrial fibrillation in the United States is expected to reach 12 million by 2050 while atrial flutter, often a result of ablative treatment, is also expected to rise as more of these treatments are administered. When pharmacological treatment fails, radiofrequency (RF) ablation is warranted, which currently constitutes a lengthy procedure with 55% success rate for single treatments. Ventricular arrhythmias such as ventricular tachycardia and ventricular fibrillation denote extremely fast and chaotic rhythms, respectively, and can cause sudden cardiac death. Arrhythmias also increase the risk of heart attack, cardiac arrest and stroke. In addition, arrhythmias can develop to congestive heart failure, i.e., when the heart can no longer produce the expected blood volume output, for which morbidity and mortality rates remain exceptionally high. Of the nearly 5 million HF patients affected in the U.S., mortality is at 50% and 75% at 5 and 10 years of diagnosis, respectively (Heart Failure Society of America). This is mainly because standard HF care such as Cardiac Resynchronization Therapy (CRT) that aims at synchronously pacing the ventricles has a failure rate of 50-70% due to lack of reliable treatment planning. Reliable conduction mapping of the arrhythmic chamber stands to significantly improve its treatment success. To this end, our group has pioneered Electromechanical Wave Imaging (EWI) that characterizes the electromechanical function throughout the four cardiac chambers. In this study, we propose to overcome current limitations by 1) developing and optimizing parallel beamforming for EWI in all four chambers and 2) applying and validating EWI for clinical treatment planning and assessment; more specifically, RF ablation for atrial fibrillation treatment and CRT for heart failure treatment. Therefore, the hypothesis of this study is that EWI with parallel beamforming will have increased sensitivity for characterization of atrial and ventricular arrhythmias for 1) treatment planning and 2) treatment assessment. Should the findings of the proposed study indicate high reliability of EWI for treatment guidance, this novel imaging system could be readily applied in a clinical setting as part of a standard protocol to increase the currently low time efficiency and success rates.